A Tour of Go Exercises

My solutions to A Tour of Go Exercises

equivalent_binary_tree.go

package main

import "golang.org/x/tour/tree"
import "fmt"

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
	walking(t, ch)
	close(ch)
}

func walking(t *tree.Tree, ch chan int) {
	if t == nil {
		return
	}
	
	walking(t.Left, ch)
	ch <- t.Value
	walking(t.Right, ch)
}

// Same determines whether the trees
// t1 and t2 contain the same values.
func Same(t1, t2 *tree.Tree) bool {
	c1 := make(chan int)
	c2 := make(chan int)
	
	go Walk(t1, c1)
	go Walk(t2, c2)
	
	for {
		v1, ok1 := <-c1
		v2, ok2 := <-c2
			
		if ok1 != ok2 || v1 != v2 {
			return false
		}
		if ok1 == false {
			break
		}
	}
	return true
}

func main() {
	ch := make(chan int)
	go Walk(tree.New(1), ch)
	for i := range ch {
		fmt.Printf("%d\n", i)
	}
	
	fmt.Println(Same(tree.New(1), tree.New(1)))
	fmt.Println(Same(tree.New(1), tree.New(2)))
}

web_crawler.go

package main

import (
	"fmt"
	"sync"
)

type Fetcher interface {
	// Fetch returns the body of URL and
	// a slice of URLs found on that page.
	Fetch(url string) (body string, urls []string, err error)
}

type Cacher struct {
	mu sync.Mutex
	m map[string]bool
}

func (c *Cacher) Cache(url string) {
	c.mu.Lock()
	c.m[url] = true
	c.mu.Unlock()
}

func (c *Cacher) Contains(url string) bool {
	c.mu.Lock()
	defer c.mu.Unlock()
	return c.m[url]
}

var cacher Cacher = Cacher{m: make(map[string]bool)}


// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher, ch chan bool) {
	// TODO: Fetch URLs in parallel.
	// TODO: Don't fetch the same URL twice.
	// This implementation doesn't do either:
	if depth <= 0 {
		ch <- true
		return
	}

	if (cacher.Contains(url)) {
		ch <- true
		return
	}

	body, urls, err := fetcher.Fetch(url)
	if err != nil {
		fmt.Println(err)
		ch <- true
		return
	}
	fmt.Printf("found: %s %q\n", url, body)
	cacher.Cache(url)
	c := make(chan bool)
	for _, u := range urls {
		go Crawl(u, depth-1, fetcher, c)
	}

	for i:=0; i < len(urls); i++ {
		<-c
	}
	ch <- true
}

func main() {
	ch := make(chan bool)
	go Crawl("https://golang.org/", 4, fetcher, ch)
	<-ch
}

// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult

type fakeResult struct {
	body string
	urls []string
}

func (f fakeFetcher) Fetch(url string) (string, []string, error) {
	if res, ok := f[url]; ok {
		return res.body, res.urls, nil
	}
	return "", nil, fmt.Errorf("not found: %s", url)
}

// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
	"https://golang.org/": &fakeResult{
		"The Go Programming Language",
		[]string{
			"https://golang.org/pkg/",
			"https://golang.org/cmd/",
		},
	},
	"https://golang.org/pkg/": &fakeResult{
		"Packages",
		[]string{
			"https://golang.org/",
			"https://golang.org/cmd/",
			"https://golang.org/pkg/fmt/",
			"https://golang.org/pkg/os/",
		},
	},
	"https://golang.org/pkg/fmt/": &fakeResult{
		"Package fmt",
		[]string{
			"https://golang.org/",
			"https://golang.org/pkg/",
		},
	},
	"https://golang.org/pkg/os/": &fakeResult{
		"Package os",
		[]string{
			"https://golang.org/",
			"https://golang.org/pkg/",
		},
	},
}